Visible seam on the mesh
It seems that half of the normals in your model are inverted (the normals of some faces are facing inward and some outward). This might be causing display problems.

Go to Edit Mode, select all faces and use CTRL + N to recalculate normals.

If recalculating the normals doesn't help, display face normals as lines, select only the faces with normals facing inward, and flip normals on those faces.